Rhyolite is an igneous silica rich volcanic rock. It's composition is typically 69% SiO2
The composition is usually quartz,sanidine and plagioclase. Rhyolite can have a texture from glassy to something along the lines of granite. The glassy types are what is used for jewelry and such. Many gemstones called jasper are actually rhyolite. one that comes to mind is Australian Rain Forest Jasper. Another Rhyolite is
the gemstone Wonder Stone.